Findings are described in 5 patients who at necropsy were found to have origin of the left main coronary artery from the right sinus of Valsalva and coursing of the anomalously arising artery between aorta and pulmonary trunk to reach the left side of the heart. Three (all boys) of the 5 patients died suddenly at 13, 14 and 19 years, respectively. 2 of them had had 1 or more episodes of syncope and the third had an abnormal electrocardiogram. The fourth patient, a 64-year-old woman, died of chronic congestive heart failure 1 year after an acute myocardial infarction. She had insignifican coronary atherosclerosis. The fifth patient, an 81-year-old man, died of chronic alcoholism, having been free of symptoms of cardiac dysfunction during life. Additionally, chinical and necropsy findings are summarized in 38 previously report necropsy patients with the coronary anomaly. Of the 38 (34 males [89%], 23 (61%) died suddenly in the first 2 decades of life; death in 6 (16%) other appears to have been related to coronary atherosclerosis and 9 patients (24%) died from non-coronary causes. Thus, this anomaly is life threatening. Why it frequently causes fatal cardiac arrest in some young individuals and allows a normal life span in other remains unclear.